How do you measure sharpness?

EdgeKit

EdgeKit

Joined
Jan 24, 2010
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I've read of descriptions like hair popping sharp, but am not sure what they are referring to. How do you measure the sharpness of a blade?
 
Hair popping is actually that. When you shave some hairs on your arm it actually causes the hairs to pop off your arm a few inches. Just shaving sharp you are almost scraping the hairs off and they just seem to stay on the knife blade. You can also get it to where you can pick a hair, put the blade to it, and cut it off above the skin by just holding the blade to the hair. This is tree topping sharp. Some people can take a hair and actually whittle it into many little curls but I think this takes quite a bit of technique.

A good way to test sharpness is to push cut newspaper. Don't slide the blade through the paper but just push so one spot is doing the cutting. If you can do this without it grabbing and ripping the paper it is pretty sharp. The further away from the point of contact you can cut the paper the sharper it is.

I usually cut paper and shave hair to get a feeling for sharpness. The more you do it the more you develop a feel for sharpness.

You can also put the blade perpendicular to your finger nail. If it bites in with little pressure it is sharp and if it slides it needs work. You can cut veggies as a sharp knife can make almost see through tomato slices. I also sometimes rub my finger tips over the edge. The way it grabs gives you a pretty good idea of sharpness but it is a learned feel. I'm sure others will chime in on their method.
 
Shave your face with it, that will tell you if it's truly sharp. You need a really sharp edge to do it without the pulling sensation.
 
FlaMtnBkr said:
Hair popping is actually that. When you shave some hairs on your arm it actually causes the hairs to pop off your arm a few inches. Just shaving sharp you are almost scraping the hairs off and they just seem to stay on the knife blade. You can also get it to where you can pick a hair, put the blade to it, and cut it off above the skin by just holding the blade to the hair. This is tree topping sharp. Some people can take a hair and actually whittle it into many little curls but I think this takes quite a bit of technique.

A good way to test sharpness is to push cut newspaper. Don't slide the blade through the paper but just push so one spot is doing the cutting. If you can do this without it grabbing and ripping the paper it is pretty sharp. The further away from the point of contact you can cut the paper the sharper it is.

I usually cut paper and shave hair to get a feeling for sharpness. The more you do it the more you develop a feel for sharpness.
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+1:thumbup:

Usually by how it removes hair i can get a pretty good grasp of what level of sharpness its at...
 
I just shave my hand, arm, etc. when it shaves like a rasor i figure its sharp enough. My left hand has been mostly bald for over a year now.

I missed a place shaving my face and noticed it in the bathroom at work, so i shaved it with my Hissatsu folder. lol
 
I'll shave some arm hairs, then do the thumbnail grab at a few points on the blade. Just using the knife is a good test too, if it doesn't perform on your material the way you like, sharpen it.
 
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The only real way I know of to measure sharpness is to use a microscope and measure the actual width of the cutting edge, as in looking straight into the sharpened edge. Scalpels start at 0.001 mm wide and razors are around half that or sharper. Of course you need some skill and access to a scanning electron microscope to do it this way.

Cutting various things will give you relative indications of sharpness. Knives that can push cut paper 2 inches from the point of hold are sharper than those that only can do it at 1 inch. I use a small scale and a wood holder to push through a piece of sewing thread. The sharpest knives I have will push through the thread at less than 20 grams. You can also fold the end of a sheet of paper so that about 1/2 inch is standing straight up. Try to push the blade straight down into the paper and cut it. If you can do that, fold up a piece 3/4 inch, then 1 inch, etc. The higher the paper you can cut, the sharper the knife. You will eventually get enough paper that it wont support it's own weight and will have to switch to another method.
 
Uz4u said:
I just shave my hand, arm, etc. when it shaves like a rasor i figure its sharp enough. My left hand has been mostly bald for over a year now.

I missed a place shaving my face and noticed it in the bathroom at work, so i shaved it with my Hissatsu folder. lol
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Arm hairs are kind of thin and you don't have many nerve receptors there so you can't detect pulling. It's too easy of a sharpness test, shaving your face is much more demanding of higher sharpness and a better test IMHO.
 
Am I the only one who drops a silk scarf onto the blade to see if its own weight will cause it to cleave? I saw Saladin do this in a movie and always thought his method was better than King Richards... :cool:

Stitchawl
 
If the edge is adequate for the task at hand, you're good to go. You only need shaving sharp if you plan to shave...
 
Push cut newpaper, then shave face, then see if I can tree top hairs or whittle hair. Most knives do NOT need to be this sharp. Most knives and people would be fine with a knife that slices computer paper easy.
 
There is also Jedi sharpness, which goes way beyond anything comprehendible to non-Jedi. These Jedi edges are so sharp that after being seen by an individual, that individual has to be careful not to think about what they have seen, or the image can cut their mind with a form of reverse Psychokinesis. Of course they have to survive the initial sight of such an edge, and many times they return from the experience completely hairless.

I have been told that they don't need sharpness tests because they "believe in the force."







That is what legend has it anyway:D.
 
The Government said:
There is also Jedi sharpness, which goes way beyond anything comprehendible to non-Jedi. These Jedi edges are so sharp that after being seen by an individual, that individual has to be careful not to think about what they have seen, or the image can cut their mind with a form of reverse Psychokinesis. Of course they have to survive the initial sight of such an edge, and many times they return from the experience completely hairless.

I have been told that they don't need sharpness tests because they "believe in the force."







That is what legend has it anyway:D.
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Lol, Jedi sharpness :D



Or you could get a scanning electron microscope.
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And the sad thing is I'd want one for just that reason. Know anyone that has one???
 
The Government said:
There is also Jedi sharpness, which goes way beyond anything comprehendible to non-Jedi. These Jedi edges are so sharp that after being seen by an individual, that individual has to be careful not to think about what they have seen, or the image can cut their mind with a form of reverse Psychokinesis.
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Yes... Edges soooo sharp that if you just look at them, your eyeballs bleed.

Fusion-powered stealth edges... I think Benchmade makes them.

Stitchawl
 
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